Olbermann, the veteran commentator and “Countdown” host, said at the end of his regular Friday broadcast it would be his last.

He did not explain why he was leaving, and NBC spokesman Jeremy Gaines said only that Comcast's acquisition of NBC Universal this week had "nothing to do" with the decision, MSNBC.com reported.

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Olbermann, MSNBC's top-rated prime-time host, said he was tempted to indulge in a broadcast newsman’s fantasy based on the movie “Network” where “you go off on an existential, other worldly, verbal journey of unutterable profundity and vision.”

Instead he began his goodbye by reminiscing on his move to MSNBC from ESPN.

"I was supposed to fill in for the late Jerry Nachman for exactly three days,” Olbermann recalled. “Forty-nine days later there was a four-year contract for me to return to this nightly 8 p.m. time-slot which I had fled four years earlier."

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Olbermann then referenced his show’s “anti-establishment” coverage of the Bush-era wars in Iraq and Afghanistan and Hurricane Katrina.

In addressing viewers, Olbermann said: “The program grew thanks entirely to your support with great rewards for me and I hope for you.”

"There were many occasions particularly in the last two and a half years where all that surrounded the show — but never the show itself — was just too much for me,” he added. “But your support and loyalty and if I may use the word insistence ultimately required that I keep going.”

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In November, Olbermann was suspended for two days after Politico reported he had donated to three Democratic candidates running for federal office.

NBC policy mandates employees of the news organization get prior permission before engaging in political activities or making donations to candidates because of potential conflicts of interest.

Olbermann maintained he did not know about the policy and that it was unevenly applied. When he returned to MSNBC he apologized to his viewers but not the network.

On Monday, “The Last Word with Lawrence O’Donnell” will move to 8 p.m. ET and “The Ed Show,” will move to 10 p.m. ET on msnbc, MSNBC.com reported.

MSNBC contributor Cenk Uygur will fill in as host at 6 p.m.

In signing off, Olbermann read from a James Thurber novel as he usually does on Fridays and gave a special thank you to the late "Meet the Press" host Tim Russert, whom he called his "greatest protector" and "cheerleader."